Blood Tests For Evaluating Arthritis

December 26, 2003

http://arthritis.about.com/cs/diagnostic/a/bloodtests.htm

CBC, Chemistry Panel, ESR, RF, HLA

General Blood Tests

* Complete Blood Count (CBC)

* Chemistry Panel

Specialized Blood Tests

* Erythrocyte Sedimentation Rate (ESR or Sedrate)

* Rheumatoid Factor (RF)

* HLA Typing

* Antinuclear Antibody (ANA)

* Lupus Erythematosus (LE) Test

* Anti-DNA and Anti-Sm

* Complement

Complete Blood Count (CBC)

The complete blood count is a test of red blood cells, white blood

cells, and platelets. Blood consists of these components suspended in a

thick, colorless fluid called plasma. Automated machines rapidly count

the cell types. The white cell count is normally between 5,000-10,000.

Increased values suggest inflammation or infection. Exercise, cold, and

stress will temporarily elevate the white cell count. Normal values for

the red cell count vary with sex. Males normally have values around 5-6

million per microliter. Females have a lower normal range at 3.6-5.6

million red cells per microliter.

Hemoglobin, the iron containing component of red cells which carries

oxygen, is also measured in a complete blood count. The normal

hemoglobin value for males is 13-18 g/dl. Normal for females is 12-16

g/dl. The hematocrit measures the percent of total blood volume which is

red cells. Normal value for males is 40-55%, and the normal value for

females is 36-48%. Generally, the hemoglobin times 3 equals the

hematocrit. Decreased values are indicative of anemia.

The MCV, MCH, MCHC are red cell indices which indicate the size and

hemoglobin content of individual red cells. These indices give clues as

to the probable cause of an existing anemia. Platelets are components

which are important in clot formation. Many drugs decrease the platelet

count or affect platelet function. Normal values range from 150,000-400,000.

The process of inflammation can cause changes in the blood count. The

red cell count may go down, the white cell count may go up, and the

platelet count may be elevated. While anemia may accompany inflammatory

arthritis it may be caused by other things such as blood loss or iron

deficiency. Only when other causes have been ruled out can a doctor

interpret blood abnormalities as a sign of inflammation.

The percent and absolute number of each type of white blood cell is

called the differential. Neutrophils are increased in bacterial

infections and acute inflammation. Lymphocytes are increased in viral

infections. Monocytes are increased in chronic infections and eosinphils

are increased in allergies. Basophils, which are generally 1 or 2% do

not usually increase.

Chemistry Panel

The chemistry panel is a series of tests which are used to evaluate

overall health. The tests include heart risk indicators, diabetes

indicators, as well as tests for kidney, liver, and thyroid function.

For example, a patient with a high creatinine level may have a problem

with the kidneys. Creatinine is a waste product found in the blood.

Certain types of inflammatory arthritis can affect kidney function.

Certain arthritis drugs can affect kidney function too. Uric acid is

another test of the blood chemistry panel which, if elevated, may be

indicative of gout.

Erythrocyte Sedimentation Rate (ESR)

The erythrocyte sedimentation rate is a test which involves placing a

blood sample in a tube and determining how fast the red blood cells

settle to the bottom in one hour. When inflammation occurs the body

produces proteins in the blood which make the red cells clump together.

Heavier cell aggregates fall faster than normal red cells. For healthy

individuals, the normal rate is up to 20 millimeters in one hour.

Inflammation increases the rate significantly. Since inflammation can be

caused by conditions other than arthritis, the sedrate test alone is not

diagnostic.

Rheumatoid Factor (RF)

Rheumatoid Factor is an antibody found in unusually large amounts of

patients with rheumatoid arthritis. Rheumatoid factor was discovered in

the 1940's and became a significant diagnostic tool in the field of

rheumatology. 80% of RA patients have RF in their blood. Usually, the

higher concentration of RF, the more severe the rheumatoid arthritis. RF

can take many months to show up in a patients blood. If tested too early

in the course of the disease, the result could be negative and retesting

should be considered at a later date. There are also patients with all

the signs and symptoms of RA but are seronegative for RF. Some doctors

suspect another disease masquerading as RA in these cases. RF can occur

in response to inflammatory of infectious diseases other than RA, though

usually in these cases, the amount is lower.

HLA Typing

White blood cells may be typed for the presence of HLA-B27. This test is

common in medical centers because it is needed for transplants. What has

been found is that this genetic marker is present in some forms of

arthritis, chiefly ankylosing spondylitis and Reiter's syndrome.

ANA, LE, Anti-DNA, Anti-Sm, Complement

Antinuclear Antibody (ANA)

Patients with certain rheumatic diseases, especially lupus, make

antibodies to the nucleus, or command center, of the body's cells. These

antibodies are called antinuclear antibodies and are tested for by

placing a patient's blood serum on a microscope slide containing cells

with visible nuclei. A substance containing fluorescent dye is added

which binds to the antibodies. Under a microscope the abnormal

antibodies can be seen binding to the nuclei. Over 95% of patients with

lupus have a positive ANA test. 50% of rheumatoid arthritis patients are

positive for ANA. Patients with other diseases also can have positive

ANA tests. Other criteria must be involved in definitive diagnosis.

Lupus Erythematosus (LE)

This test is not commonly performed anymore. Its initial discovery

opened up the whole field of antinuclear antibodies though. Only 50% of

lupus patients are found to have positive LE tests. Therefore the test

does not identify 50% of patients as having the disease.

Anti-DNA and Anti-Sm

Lupus patients have antibodies to the heredity material DNA

(deoxyribonucleic acid). It is a useful diagnostic tool since it is

unusual to find these antibodies in people who do not have lupus. The

test is also a good monitoring tool since the levels of anti-DNA rise

and fall with disease activity.

Lupus patients also have antibodies to Sm, another substance in the

cell's nucleus. These antibodies also occur only in lupus patients. The

test is not particularly useful in monitoring disease activity however.

Complement

The complement system is a complex set of blood proteins which are part

of the body's defense system. These proteins are inactive until an

antibody binds to an antigen and activates the complement system. The

system produces factors which help destroy bacteria, and combat invaders

with white cells. These reactions consume complement and leave depressed

levels indicative of immune complex formation. Lupus patients often show

decreased levels of total complement. The complement test may be helpful

in tracking the disease activity of a lupus patient.

Laboratory blood tests are valuable diagnostic tools. They are usually

not definitive when considered alone. The entire clinical picture of a

patient, and the patient's history must be evaluated along with

laboratory test results in order to produce an accurate diagnosis.

REFERENCES:

The Duke University Medical Center Book Of Arthritis, by S.

Pisetsky, M.D., Ph.D.

~ Carol Eustice

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February 12, 2008

Not sure if any of this helps, but it is something I kept to help

understand blood tests.